Geometric Dimensioning and Tolerancing (GD&T) is the language that links design, production and metrology: applied well, it helps ensure a part assembles and functions as intended; misread, it produces conflicting measurements, scrap and costly back-and-forth between teams. In a contributed article, Metrologic DCS argues that the risk is growing as Product Manufacturing Information (PMI) is increasingly embedded in CAD files and as standards keep evolving, and sets out four practices intended to make the chain from design intent to shop-floor reporting more reliable.
Treat the PMI as the starting point
Working from PMI requires decoding the design intent: which feature is targeted, which references apply and which tolerance is specified. Done manually, the company says, this step is error-prone — a value copied incorrectly or a reference misunderstood means the part is inspected against a requirement that was never specified. Its recommendation is to use software that takes the PMI as its starting point rather than asking the user to re-enter tolerances, so that features and their evaluations are created from the part's digital definition. The stated result is no re-keying, fewer interpretation gaps and time saved at the first step of program preparation.
Do not rebuild datum reference frames by hand
The Datum Reference Frame (DRF) defines where measurement starts. It is made up of reference features (A, B and C) and determines which of the part's degrees of freedom are constrained for the evaluation. If the frame is built in the wrong order, or the degrees of freedom are poorly selected, the same part can be declared conforming or non-conforming depending on the operator — which Metrologic DCS identifies as a major source of GD&T misinterpretation. Automating the step so that the DRF and its degrees of freedom follow from the drawing definition rather than from the operator's choice is presented as the way to make results repeatable across operators, machines and sites. In the company's Metrolog software, the DRF is created automatically when a GD&T is evaluated, and the degrees of freedom are selected accordingly.
Reuse imported DRFs to limit rework
Reference features are already defined in the CAD model, where A, B and C carry labels placed by the design office. Recreating them during program preparation wastes time, opens the door to discrepancies and forces rework whenever the definition changes; on a part with many annotations it is also hard to see which have already been handled and which still need measuring. The advice is to start from the DRFs carried by the PMI and predefine the GD&T from them, while keeping a clear view of progress — where each annotation sits on the part and where its measurement stands. In Metrolog, the Scan GDT function reads the decoded PMI and assigns a status, so that both the decoding and the measurement can be validated.
Make reports actionable for the shop floor
A report limited to “pass” or “fail” does not tell the shop floor what to do; if the machine operator cannot tell what kind of defect is present, adjustments become trial and error, producing scrap and correction loops. The article recommends tailoring the output to its reader: a table of numerical values for quality control, a Go/No-Go report where a quick decision is needed, and a decomposition analysis for the operator. Metrolog splits the defect of an evaluated feature into four independent types — form, size, position and orientation — alongside the global defect, so that the dominant type, and therefore what to correct first, becomes visible.
Scope of the guidance
The four recommendations are vendor guidance drawn from the company's own software practice, and the article offers no case data, measured results or customer examples. Claims such as fewer interpretation gaps, time saved in program preparation and reduced scrap are stated as expected outcomes of the described workflow rather than independently verified figures. The failure points it describes — manual re-entry of tolerances, hand-built datum frames and pass/fail-only reporting — remain the practical targets the workflow is meant to address.